Project Summary Hearing perception relies on our ability to tell apart the spectral content of different sounds, and to learn to use this difference to distinguish behaviorally relevant (such as dangerous and safe) sounds. The primary auditory cortex (A1) has been shown to play an important modulatory role in frequency discrimination and auditory discriminative emotional learning. However, despite decades of research that have carefully mapped the auditory response properties of neurons in A1, the neuronal circuits that underlie this modulation are currently unknown. The goal of the proposal is to test the role of such candidate neuronal circuit. In this proposal, we test the hypothesis that the activity of the most common class of interneurons, parvalbumin- positive (PVs), modulates selectivity to tones at different frequencies of excitatory neurons in A1, and that PV activity affects the behavioral performance in frequency discrimination and precision of discriminative auditory emotional learning. To measure the effect of PV activity we activate or inhibit PV interneurons selectively and temporally precisely using a recently developed optogenetic system, in awake behaving mice, and compare the neurometric and behavioral performance during activation or inactivation of PVs to baseline condition.